In a telecommunication network a call initiated by a calling entity to a called entity may not result in a successful connection between the two entities. For example, the called entity may be involved in another call, i.e. is busy, or is unable to answer the call at the time the call is made. In addition in mobile networks, the call may fail because the called entity may be not reachable for some reason. For example, the called entity may be located in an area that is shielded from radio reception or the called entity's user equipment may be turned off.
When a first call attempt fails, the calling entity can initiate a second call attempt at a later time. As the calling entity usually will not know when the circumstances that prevented the first call attempt from being completed have been corrected or changed, it is not uncommon that the calling entity may have to make several further call attempts before the call is finally completed.
In order to provide greater convenience to their subscribers, telecommunication service providers offer call completion services for use in situations where a call is not completed due to the called entity being unavailable, e.g. busy or not reachable. An example is the supplementary service Completion of Calls to Busy Subscriber (CCBS). CCBS has been specified for example in 3GPP (3rd Generation Partnership Project) TS (Technical Specification) 22.093.
When the called entity is busy or not reachable, the call completion services are typically designed to offer the calling entity an automatic call back when the called entity becomes available for the call back. Usually a switching node, such as a mobile switching center (MSC), that is serving the calling entity will offer the calling entity the option of an automatic call back when the called entity appears to be unavailable, e.g. busy or not reachable. If the calling entity accepts the offer, a procedure is started by a switching node serving the called entity for monitoring the availability of the called entity. As soon as it is detected that the called entity is available or idle again, i.e. no longer busy or in back radio contact with the network, then the switching entity serving the calling entity is notified. This switching entity will initiate a call towards the calling entity and if the calling entity answers, the call is set up to the called entity. Alternatively, the switching entity sends a designated notification to the calling entity, informing the calling entity that the called entity is now available, upon which the calling entity may initiate the establishment of the call to the called entity
In addition to so-called network based services such as call completion services, i.e. services executed by and under the control of switching nodes, there are also Intelligent Network services that are executed and controlled by an Intelligent Network (IN). According to the IN concept, service intelligence or service logic is separated from switching functions. This separation basically enables network operators to develop and deploy services and features independently of vendors, allowing more flexibility in service development, simplified rollout, reduced costs and greater autonomy. Examples of IN protocols are the Intelligent Network Application Protocol (INAP), the Advanced IN (AIN), and the Customized Applications for Mobile network Enhanced Logic (CAMEL). INAP was developed for fixed line networks and is the primary protocol used for fixed line IN outside of North America. AIN is a variant developed for North America.
CAMEL is a Global System for Mobile communications (GSM) Phase 2+ and Wideband Code Division Multiple Access (WCDMA) network feature specified in 3GPP TS 22.078. CAMEL is based on core INAP with modifications to take into account, amongst others, subscriber mobility. In particular, CAMEL enables the use of operator-specific services by a subscriber even when roaming outside the subscriber's Home Public Land Mobile Network (PLMN). A CAMEL-based Intelligent Network comprises as main entities a service switching entity for switching tasks, also referred to as SSF (Service Switching Function) or gsmSSF (GSM Service Switching Function) and a service control entity comprising the service intelligence or logic also referred to as SCP (Service Control Point) or gsmSCF (GSM Service Control Function).
FIG. 1 depicts a schematic overview of a telecommunications network comprising an Intelligent Network according to the prior art.
The Intelligent Network comprises a service control point 101 and a service switching function 102. Furthermore, switching nodes MSC 103, MSC 104 and MSC 105 are depicted, each of which may be a Mobile Switching Centre (MSC). MSC 103 is serving the calling entity and MSC 105 is serving the called entity. FIG. 1 further depicts a calling entity CE100 and a called entity CE106.
Intelligent Networks services are executed by and under the control of the service control point 101. The service control point 101 is able to communicate with the service switching function 102 using an Intelligent Network protocol such as CAMEL or INAP. The service switching function 102 of this example is co-located at switching node 103, i.e. the switching node serving the calling entity. Alternatively, the service switching function 102 may be implemented as a separate node.
Call completion services as stated before, are network based services that are executed by and under control of switching nodes, whereas IN services are executed under the control of a service control entity and invoked for certain calls only. Because of the two levels of control that are also separate from each other, inconsistencies may occur when an IN service is invoked for a call that may be in addition subject to a call completion service. This may lead to call completion failures.